An important concern for any analog circuit design is noise, which is often measured in terms of a signal to noise ratio (SNR) parameter for the circuit. The presence of noise in a circuit degrades the precision of analog signals as well as other performance-related parameters for the circuit. Consequently, it is often desirable to minimize noise in most analog circuit designs.
As is inherent from a signal to noise ratio parameter, noise effects are typically minimized by decreasing the level of noise and/or by increasing the level of the signal relative to noise. However, due to other competing concerns, such as total harmonic distortion (THD) and/or signal delays, e.g., due to phase shifting, the ability to increase the SNR of an analog circuit by conventional methods may be limited.
For example, one analog circuit in which noise minimization is desired is a continuous time low pass anti-aliasing filter in a partial response maximum likelihood (PRML) read/write channel of a hard disk drive system. It is desirable in such circuits to increase SNR and decrease THD to minimize the bit error rate (BER) of the channel. Consequently, the goal in such circuits is often to keep the signal swing as large as possible without causing distortion.
However, another important concern for many analog circuit designs is that of the effects of temperature, since analog circuits may be required to operate over wide operating ranges. Due to temperature dependencies in many analog circuit components, e.g., transistors, operational parameters including but not limited to gain, SNR, effective linear signal range--the maximum permissible input signal level to a component which does not cause distortion--may vary. This often requires such analog circuits to be designed for worst case operation, which limits the overall performance of such circuits over their entire operating ranges.
For example, in many low pass filter and other analog circuit designs, the effective linear signal range of the circuits may vary directly with temperature. Often, the signal swings of the inputs to such circuits must be set to levels which do not cause distortion at colder temperatures, even though the effective linear signal ranges of such circuits may be greater at their normal operating temperatures.
Therefore, a significant need exists for a manner of optimizing the performance of analog circuits over a range of operating temperatures.